In these days, neodymium magnets that contain a large amount of rare earth such as expensive dysprosium (Dy) are used to obtain high coercive force properties in rotating electric machines that are used to drive a vehicle. However, in association with the recent hike in prices of such rare earth, there are demands for high-performance rotating electric machines in which the demagnetizing capacity is restrained from being reduced or lost even though the contents of dy is reduced or no dy is contained.
For example, Patent Literature 1 proposes an IPM motor rotor having plural permanent magnets that are embedded in a rotor core in which the demagnetizing capacity of the embedded permanent magnets is attempted to be improved. As shown in FIG. 11, in a rotor 100 of this rotating electric machine, plural pairs of permanent magnets 117A, 117B are accommodated in corresponding permanent magnet accommodating portions 119A, 119B that have voids 120A, 120B at end portions thereof, respectively, in such a way that each pair of permanent magnets 117A, 117B are disposed substantially in a V-shaped fashion. Plural slits 121A, 122A, 123A and plural slits 121B, 122B, 123B are disposed between portions of magnetic pole surfaces 170A, 170B of the permanent magnets 170A, 170B that lie near magnetic pole end portions 172A, 172B and an outer circumferential surface 162 of a rotor core 160 in such a way as to be substantially perpendicular to the magnetic pole surfaces 170A, 170B. Radial lengths of the slits 121A, 122A, 123A and the slits 121B, 122B, 123B are gradually increased to be longer in the order in which the slits are aligned from central portions to the magnetic pole end portions 172A, 172B of the magnetic surfaces 170A, 170B of the permanent magnets 117A, 117B. The slits 121A, 122A, 123A and the slits 121B, 122B, 123B restrict magnetic fluxes that are produced from the central portions of the magnetic pole surfaces 170A, 170B from propagating towards portions between the magnetic pole end portions 172A, 172B and the outer circumferential surface 162 of the rotor core to thereby suppress the occurrence of magnetic saturation at portions near the magnetic pole end portions 172A, 172B of the permanent magnets 117A, 117B, whereby an improvement in demagnetizing capacity is attempted.
In addition, in a rotor described in Patent Literature 2, a single void is provided at each of end portions of a longitudinal outer circumferential side of a rectangular permanent magnet on a side facing an outer circumference of the rotor as a short-circuit preventing unit that prevents the formation of a magnetic flux short-circuit so as to increase the magnetic resistance at both the end portions of the magnet to thereby prevent the occurrence of a short-circuit in magnetic flux between end portions of adjacent permanent magnets, so that the torque of the magnet can be used effectively.